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Date: Mon, 17 May 2010 11:09:31 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: Haicheng Li <haicheng.li@linux.intel.com>
cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>,
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       Andi Kleen <andi@firstfloor.org>, Mel Gorman <mel@csn.ul.ie>,
       Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 3/3] mem-hotplug: fix potential race while building
 zonelist for new populated zone
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On Mon, 17 May 2010, Haicheng Li wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 72c1211..0729a82 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2783,6 +2783,20 @@ static __init_refok int __build_all_zonelists(void
> *data)
>  {
>  	int nid;
>  	int cpu;
> +#ifdef CONFIG_MEMORY_HOTPLUG
> +	struct zone_online_info *new = (struct zone_online_info *)data;
> +
> +	/*
> +	 * Populate the new zone before build zonelists, which could
> +	 * happen only when onlining a new node after system is booted.
> +	 */
> +	if (new) {
> +		/* We are expecting a new memory block here. */
> +		WARN_ON(!new->onlined_pages);
> +		new->zone->present_pages += new->onlined_pages;
> +		new->zone->zone_pgdat->node_present_pages +=
> new->onlined_pages;
> +	}
> +#endif


Building a zonelist now has the potential side effect of changes to the
size of the zone?

Can we have a global mutex that protects against size modification of
zonelists instead? And it could also serialize the pageset setup?